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Size dependent sensitivity of Yb,Er up-converting luminescent nano-thermometers

Abstract

The non-contact temperature sensing using luminescence intensity ratio (LIR) between 2H11/2→4I15/2 and 4S3/2→4I15/2 electronic transition in upconverting Yb3+ and Er3+ co-doped nanocrystals has been known for two decades. The phenomenon is governed by simple Boltzmann formula, which however does not consider material’s properties other than energy gap between the respective energy states. For example the temperature sensitivity has never been shown to depend from the size of nanoparticles, however our studies, performed on two different NaYF4:Er3+,Yb3+ and LiLaP4O12:Er3+,Yb3+ nanocrystals clearly show evidences of such relationship. Upon constant excitation intensity, the changes of LIR emission intensity ratio in response to rising external temperature become consistently more rapid for smaller nanocrystals. It was found that sensitivity of up-converting luminescent thermometer changes proportionally to the nanoparticles’ sizegrain size, i.e. raised from 1.1 %/K @ 240 nm to 1.8%/K @ 20 nm nanocrystals for tetraphosphates and similarly raised from 1.1%/K @ 200 nm to 2.1 %/K @ 8 nm fluoride nanocrystals at 200 K. These phenomena were manifested mainly at low temperatures and can be neglected at temperatures above 250 K. The observed changes were discussed in terms of nonradiative surface-quenching of the 4S3/2 state. Phenomenological models have been proposed to describe both, size dependent luminescence lifetimes and temperature sensitivity.

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Publication details

The article was received on 26 May 2017, accepted on 12 Jul 2017 and first published on 14 Jul 2017


Article type: Paper
DOI: 10.1039/C7TC02322G
Citation: J. Mater. Chem. C, 2017, Accepted Manuscript
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    Size dependent sensitivity of Yb,Er up-converting luminescent nano-thermometers

    L. Marciniak, K. Prorok and A. Bednarkiewicz, J. Mater. Chem. C, 2017, Accepted Manuscript , DOI: 10.1039/C7TC02322G

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